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A novel hexafla vonoid from Lophira alata
TETRAHEDRON LETTERS TetrahedronLetters40 (1999) 4721-4724
Pergamon
A NOVEL HEXAFLAVONOID A. Ewola
Tiha,
a Center for Recherch b Department cLaboratoire
Absfract
: From
of Organic de
the MeOH
R. Ghogomu
on Medicinal
B.L. Sondengamb*,
plants and of Traditionnal
Chemistry Chimie.
Tihb,
FROM LOPHIRA ALATA.
, University UA
401.
of Yaounde
CNRS,
Mu&urn
M.T.
Mcdecine,
Martinc,
B. Bodoc
P.O. Box. 11126 Yaouude.
1, P.O. Box. 812. Yaouude, National
d’Histoire
63 Rue Buffon, 7500.5 Paris, France. Received 6 January1999; accepted27 April 1999 extract of the stem bark of Lophira alafu a hexatlavcnoid
the structure of which has been elucidated by spectroscopic 0 1999 Published by Elsevier Science Ltd. All rights reserved.
Cameroon. Naturelle,
has been isolated,
and chemical
evidence.
Previous investigations{ 1,2,3,4}, have shown that the methanolic extract of the stem bark of Lophiraalata Banks ex Gaertn contains many very polar new polyflavonoids, some having important antibacterial and antiviral activities. These.interesting results made us examine a more polar fraction of the sameextract, which after purification by repeated chromatography over silica gel, gave 1Omg of an amorphous light brown solid, Azobechalcone l the structure of which is reported in this paper. Azobechalcone 1, showed a positive flavonoid test and was attributed the molecular formula C&-I7&2, from HR-FAB+-MS analysis in which the (M+H)+ appeared at m/z 1503.4439 (Calculated Cs,$-I7sq2 requires 1503.4436). Strong absorptions observed in its IR spectrum (KBr paste) at 3460 cm-r (hydroxyl) , 1635cm-1(conjugated and chelated carbonyl) and 1618 cm-l (conjugated aromatic double bonds) are consistent with a flavonoid structure. Its 300 MHz rH NMR spectra (1D and 2D COSY) had signals defining the following proton systems: four 1.4 - disubstituted benzene rings; four 1,2,4 - trisubstituted benzene rings; two 1,2,4,5 - tetrasubstituted benzene rings; two benzodihydrofuran rings; one tetrasubstituted tetrahydrofuran ring; two @artsdouble bonds; two methine protons; two methylene protons; three strongly chelated hydroxyl groups at 12.761, 13.552 and 13.521 ppm typical of hydroxyl functions peri to carbonyl groups. Azobechalcone has a total of 16 hydroxyl groups since its total methylation (CHsI/ K2CQ) gave a mixture of three compounds among which a major band, recovered by prep.TLC on SiO2 support showed no residual hydroxyl IR absorption. Its rH NMR spectrum showed distinct signals for 16 CHsO groups (oppm: 3.349, 3.581, 3.589, 3.598, 3.611, 3.619, 3.641, 3.658, 3.672, 3.729, 3.752, 3.774, 3.781, 3.869, 3.878, 3.887, each 3H). Detailed analysis of the COSY LR rH NMR spectra of Azobechalcone established the fact that three biflavonoid substructures( I, II and III) were implicated in its structure such that I and II are similar to lophirone C (5) while III is closely related to mbamichalcone{ 1). Correlation spots observed between proton Hsn*(ring B4, Gppm: 7.959 ) and the proton I+r(o 4.979 ppm), locates the first interflavonoid bond linking I and II using carbons Cl(GCppm: 43.4) and C&Cppm:
0040-4039/99/$ - seefront matter0 1999 Publishedby ElsevierScienceLtd. All rightsreserved. SOO40-4039(99)00832-1
PII:
J(Hz)
complex;
6”’ (B2)
* AA’BB’
5”’
4”’
032) 02)
;I:‘(%;
d(2.4)
Multiplicity: S=
1”’ 2”‘( 3”’ 4”’ 5”’ 6”’
c’2
;‘;
(B4) (B4)
034)
(B4) B4) (B4)
122.2 154.9 103.1 154.9 121.8 131.8
s s d s s d
s d d s d d d d d
s s d s d d
s
s d s s d d d d
J(Hz)
7.959
6.494
6.544 6.970 4.656 5.661 4.7%
6.970 6.544
6.545 7.795
6.324
6.652 7.329 7.573 7.066
6.641
GHppm
Q),
s
s
m* m* dd(3.0; 11.3) d(3.0) d( 11.3)
m* m*
dd(8.8; 2.3) d(8.8)
d(2.3)
d(8.1) dd(8.1; 1.8) d( 15.3) d( 15.3)
d( 1.8)
singulet ; d= doublet ; t= triplet ; m= mulhplet.
6.288 dd( 2.4; 8.0) 7.069 d(8.0)
6.288
m* m* dd(4.0; 11.8) d(4.0) d( 11.8)
133.7 128.7 116.2 158.2 116.2 128.7 53.5 90.7 40.3
s s d s d d
6.856 7.008 4.329 5.471 4.979
1” (A41 2”( A4) 3” (~44) 4” (A41 5” b44) 6” b44)
121.1 156.2 103.1 157.6 107.7 130.1
1”’ 032)
C’l
;‘;
5” (AZ) 6” b42)
ifl g:;
7.-&X3 m* 6.856 m*
dd( 8.9; 2.1) d( 8.9)
d(2.1)
s d d s d d d d d
(A21 A2)
6.633 7.872
6.321
133.0 128.4 115.9 158.1 115.9 128.4 51.0 90.5 43.4
2;’
1”
:: ((BB:j
3’ (Bl) 4’ @I)
1’ U33) 2’ 03) 3’ 033) 4’ V33) 5’ @3) 6’ 033)
114.4 167.0 103.6 165.3 110.1 133.7
2’ @I)
s s d s d d
a2 82
6 b43)
114.3 167.0 103.2 165.3 109.3 133.1
8.2) 8.2; 1.8) 15.2) 15.2)
2( A3)
3 @3) 4 b43) 5 (A3)
127.4 125.7 132.6 163.1 109.8 133.0 117.3 145.5
GCppm:
1’ @I)
d( dd( d( d(
d( 1.8)
Carbon Nc 1 (A3)
with solvent acetone
192.3
6.762 7.452 7.168 7.720
6.641
6Hppm
and lH : 300 Mz
192.2 s
s d s s d d d d
( 13C: 7.5.6M.z
cl
Bl
ai
6641)
5 (A:)
“4g1;
127.9 126.0 132.6 162.8 109.0 132.5 117.4 145.4
Gcppm:
Nl
Carbon
1 (AI) 2( Ad
1: NMR DATA
TABLE
@s)
B6)
3”’ (B6) I”’ @6) 5”’ (B6) 5”’ (B6)
2”‘(
1”’ (B6)
: ‘3
F3
6” 646)
;” I, ;i;{
1” (A61 2”( -46) 3” c46)
6’
3’ W 4’ @5) 5’ (Bs)
2’ 035)
1’ W
a3 f%
6 (AS)
3 (As) 4 (As) 5 (AS)
Carbon NI 1 (Ad 3 AS)
113.4 166.2 103.4 165.4 108.3 .33.7
132.3 128.1 116.2 157.9 (16.2 128.1 60.0 84.6 !05.3
117.6 153.4 103.5 155.5 121.2 127.5
s s d s d d
d d d d s
s d d
s s d s s d
J(Hz)
5.954 6.459
6.157
-
6.704 7.163 3.738 5.269
7.163 6.704
7.670
6.426
6.815 6.572 6.572 6.815 3.306 2.564 2.146 5.543
8Hppm
s d d s d d d t a: b: 81.8 d
131.5 131.2 116.0 156.4 116.0 131.2 52.2 36.7
Kppm:
dd(8.9; 2.4) d(8.9)
d(2.4)
dd(9.0; 8.2) d(8.2 )
;:
S
S
m* m* dddd(5,l; 8.4; 9.0; 9.1) dd(5,l; 13.9) dd(13,9; 9,l) d( 8.4)
m* m*
4723
121.8). Connections between proton Hs (ring Bs, 6ppm:7.670 ) and proton Hc2 (6 4.7%ppm ) show that the link with III is with carbons c’s(BCppm: 40.3) and Cs* (ring Bs, BCppm: 121.2) leading to structure 1 for Azobechalcone.
-
More evidence in support of structure 1, for Azobechalcone came from its 75.6 MHz CMR spectra in which complete assignments of signals were made using totally decoupled, J-modulated, as well as HMBC spectra. Signals for all 90 carbon atoms in molecular formular gave chemical shifts very similar to corresponding ones in either lophirone C or mbamichalcone. Major differences observed concerned carbons C’l and C ‘2 carbonyls in lophirone C( Kppm: 201.4 ppm) but reduced in 1 to saturated methine carbons ( GCppm: C’l=43.4 and C’+o.3) . The fragmentation pattern in the MS of Azobechalcone reflects structure 1. Interflavonoid bond cleavage in (M+H)+ ion at 1503 accounts for abundant ions at m/z 1007 and m/z 615. The base peak at m/z 1129 comes from the rupture of the bond between carbons olt and Cip while other important ions at m/z 755 and m/z 619 are accounted for in Scheme 1. An all frans stereochemistry of the pentacyclic heterocyclic protons in l, was evident as corresponding protons to those in either lophirone C or mbamichalcone having practically the same chemical shifts and coupling constants are in an all PUKVstereochemistry. Confirmation came from NOE differences measurements in which no correlation spots were observed between: H,lI and HpI Hal2 and Hp2; and finally Hp2 and H,l2 Equally, protons Hc3 and Ha3; Hd3 and H,y3; Ha*3 and Hp3 show very faint enhancements in accord with a trans - rruns trans stereochemistry of the tetrahydrofuran ring. Biosynthetically, Azobechalcone can be considered to originate from the condensation of a unit each of lophirone C and lophirachalcone (6)
4124
G,
HZ7 O9 mlz
615
HO
C67H530,7
m/z
( M+H
1129
)+
C,,H71022
m/z
1503
CsaH,,0,5
m/z
1007
HO
Cd5Ha9 O,,
m/z
C38H35 OS,
755
m/z 619
Scheme 1: Major fragments in MS of 1 ACKNOWLEGDEMENTS: We thank MM. Nolt Internatiod
CRF’MT,
Foundation
Yaounde
of Science
for harvest and identification
(grant
1389/2) and DAGIC
of plant material.
This work was supported
(France).
REFERENCES: 1) A. E. Tih, R.Ghogomu
Tih, B.L. Sondengam,
M.T.Martin
and B.Bodo,
2) A. E. Tih, R.Ghogomu
Tih, B.L.Sondengam,
M.T.
and B.BodoJ.
R. Ghogomu
Tih, B.L. Sondengam,
4) A. E. Tih, R. Ghogomu
3) A. E. Tih,
Tih, B.L. Sondengam,
Martin
M.T. Martin M.T.
Martin
Tefmhedon
Leftem : 4 5, S797, (1988).
Nat. Products
and B.Bodo,
Phyfochemismy
and B.Bodo,
Phytochemisby
5) R. GhogomuTih,
B.L. Sondengam,
M.T.
Martin
and B.Bodo.
Phyfochemistry
6) R. GhogomuTih,
B.L. Sondengam,
M.T.
Martin
and B.Bodo.
Temhedon
: 5 3,964,
(1990).
: 3 1,981, : 3 1.3595,
: 28, 15.57, (1989). Leers
: 30, 1808, (1989).
(1992). (1992).
by
Pergamon
A NOVEL HEXAFLAVONOID A. Ewola
Tiha,
a Center for Recherch b Department cLaboratoire
Absfract
: From
of Organic de
the MeOH
R. Ghogomu
on Medicinal
B.L. Sondengamb*,
plants and of Traditionnal
Chemistry Chimie.
Tihb,
FROM LOPHIRA ALATA.
, University UA
401.
of Yaounde
CNRS,
Mu&urn
M.T.
Mcdecine,
Martinc,
B. Bodoc
P.O. Box. 11126 Yaouude.
1, P.O. Box. 812. Yaouude, National
d’Histoire
63 Rue Buffon, 7500.5 Paris, France. Received 6 January1999; accepted27 April 1999 extract of the stem bark of Lophira alafu a hexatlavcnoid
the structure of which has been elucidated by spectroscopic 0 1999 Published by Elsevier Science Ltd. All rights reserved.
Cameroon. Naturelle,
has been isolated,
and chemical
evidence.
Previous investigations{ 1,2,3,4}, have shown that the methanolic extract of the stem bark of Lophiraalata Banks ex Gaertn contains many very polar new polyflavonoids, some having important antibacterial and antiviral activities. These.interesting results made us examine a more polar fraction of the sameextract, which after purification by repeated chromatography over silica gel, gave 1Omg of an amorphous light brown solid, Azobechalcone l the structure of which is reported in this paper. Azobechalcone 1, showed a positive flavonoid test and was attributed the molecular formula C&-I7&2, from HR-FAB+-MS analysis in which the (M+H)+ appeared at m/z 1503.4439 (Calculated Cs,$-I7sq2 requires 1503.4436). Strong absorptions observed in its IR spectrum (KBr paste) at 3460 cm-r (hydroxyl) , 1635cm-1(conjugated and chelated carbonyl) and 1618 cm-l (conjugated aromatic double bonds) are consistent with a flavonoid structure. Its 300 MHz rH NMR spectra (1D and 2D COSY) had signals defining the following proton systems: four 1.4 - disubstituted benzene rings; four 1,2,4 - trisubstituted benzene rings; two 1,2,4,5 - tetrasubstituted benzene rings; two benzodihydrofuran rings; one tetrasubstituted tetrahydrofuran ring; two @artsdouble bonds; two methine protons; two methylene protons; three strongly chelated hydroxyl groups at 12.761, 13.552 and 13.521 ppm typical of hydroxyl functions peri to carbonyl groups. Azobechalcone has a total of 16 hydroxyl groups since its total methylation (CHsI/ K2CQ) gave a mixture of three compounds among which a major band, recovered by prep.TLC on SiO2 support showed no residual hydroxyl IR absorption. Its rH NMR spectrum showed distinct signals for 16 CHsO groups (oppm: 3.349, 3.581, 3.589, 3.598, 3.611, 3.619, 3.641, 3.658, 3.672, 3.729, 3.752, 3.774, 3.781, 3.869, 3.878, 3.887, each 3H). Detailed analysis of the COSY LR rH NMR spectra of Azobechalcone established the fact that three biflavonoid substructures( I, II and III) were implicated in its structure such that I and II are similar to lophirone C (5) while III is closely related to mbamichalcone{ 1). Correlation spots observed between proton Hsn*(ring B4, Gppm: 7.959 ) and the proton I+r(o 4.979 ppm), locates the first interflavonoid bond linking I and II using carbons Cl(GCppm: 43.4) and C&Cppm:
0040-4039/99/$ - seefront matter0 1999 Publishedby ElsevierScienceLtd. All rightsreserved. SOO40-4039(99)00832-1
PII:
J(Hz)
complex;
6”’ (B2)
* AA’BB’
5”’
4”’
032) 02)
;I:‘(%;
d(2.4)
Multiplicity: S=
1”’ 2”‘( 3”’ 4”’ 5”’ 6”’
c’2
;‘;
(B4) (B4)
034)
(B4) B4) (B4)
122.2 154.9 103.1 154.9 121.8 131.8
s s d s s d
s d d s d d d d d
s s d s d d
s
s d s s d d d d
J(Hz)
7.959
6.494
6.544 6.970 4.656 5.661 4.7%
6.970 6.544
6.545 7.795
6.324
6.652 7.329 7.573 7.066
6.641
GHppm
Q),
s
s
m* m* dd(3.0; 11.3) d(3.0) d( 11.3)
m* m*
dd(8.8; 2.3) d(8.8)
d(2.3)
d(8.1) dd(8.1; 1.8) d( 15.3) d( 15.3)
d( 1.8)
singulet ; d= doublet ; t= triplet ; m= mulhplet.
6.288 dd( 2.4; 8.0) 7.069 d(8.0)
6.288
m* m* dd(4.0; 11.8) d(4.0) d( 11.8)
133.7 128.7 116.2 158.2 116.2 128.7 53.5 90.7 40.3
s s d s d d
6.856 7.008 4.329 5.471 4.979
1” (A41 2”( A4) 3” (~44) 4” (A41 5” b44) 6” b44)
121.1 156.2 103.1 157.6 107.7 130.1
1”’ 032)
C’l
;‘;
5” (AZ) 6” b42)
ifl g:;
7.-&X3 m* 6.856 m*
dd( 8.9; 2.1) d( 8.9)
d(2.1)
s d d s d d d d d
(A21 A2)
6.633 7.872
6.321
133.0 128.4 115.9 158.1 115.9 128.4 51.0 90.5 43.4
2;’
1”
:: ((BB:j
3’ (Bl) 4’ @I)
1’ U33) 2’ 03) 3’ 033) 4’ V33) 5’ @3) 6’ 033)
114.4 167.0 103.6 165.3 110.1 133.7
2’ @I)
s s d s d d
a2 82
6 b43)
114.3 167.0 103.2 165.3 109.3 133.1
8.2) 8.2; 1.8) 15.2) 15.2)
2( A3)
3 @3) 4 b43) 5 (A3)
127.4 125.7 132.6 163.1 109.8 133.0 117.3 145.5
GCppm:
1’ @I)
d( dd( d( d(
d( 1.8)
Carbon Nc 1 (A3)
with solvent acetone
192.3
6.762 7.452 7.168 7.720
6.641
6Hppm
and lH : 300 Mz
192.2 s
s d s s d d d d
( 13C: 7.5.6M.z
cl
Bl
ai
6641)
5 (A:)
“4g1;
127.9 126.0 132.6 162.8 109.0 132.5 117.4 145.4
Gcppm:
Nl
Carbon
1 (AI) 2( Ad
1: NMR DATA
TABLE
@s)
B6)
3”’ (B6) I”’ @6) 5”’ (B6) 5”’ (B6)
2”‘(
1”’ (B6)
: ‘3
F3
6” 646)
;” I, ;i;{
1” (A61 2”( -46) 3” c46)
6’
3’ W 4’ @5) 5’ (Bs)
2’ 035)
1’ W
a3 f%
6 (AS)
3 (As) 4 (As) 5 (AS)
Carbon NI 1 (Ad 3 AS)
113.4 166.2 103.4 165.4 108.3 .33.7
132.3 128.1 116.2 157.9 (16.2 128.1 60.0 84.6 !05.3
117.6 153.4 103.5 155.5 121.2 127.5
s s d s d d
d d d d s
s d d
s s d s s d
J(Hz)
5.954 6.459
6.157
-
6.704 7.163 3.738 5.269
7.163 6.704
7.670
6.426
6.815 6.572 6.572 6.815 3.306 2.564 2.146 5.543
8Hppm
s d d s d d d t a: b: 81.8 d
131.5 131.2 116.0 156.4 116.0 131.2 52.2 36.7
Kppm:
dd(8.9; 2.4) d(8.9)
d(2.4)
dd(9.0; 8.2) d(8.2 )
;:
S
S
m* m* dddd(5,l; 8.4; 9.0; 9.1) dd(5,l; 13.9) dd(13,9; 9,l) d( 8.4)
m* m*
4723
121.8). Connections between proton Hs (ring Bs, 6ppm:7.670 ) and proton Hc2 (6 4.7%ppm ) show that the link with III is with carbons c’s(BCppm: 40.3) and Cs* (ring Bs, BCppm: 121.2) leading to structure 1 for Azobechalcone.
-
More evidence in support of structure 1, for Azobechalcone came from its 75.6 MHz CMR spectra in which complete assignments of signals were made using totally decoupled, J-modulated, as well as HMBC spectra. Signals for all 90 carbon atoms in molecular formular gave chemical shifts very similar to corresponding ones in either lophirone C or mbamichalcone. Major differences observed concerned carbons C’l and C ‘2 carbonyls in lophirone C( Kppm: 201.4 ppm) but reduced in 1 to saturated methine carbons ( GCppm: C’l=43.4 and C’+o.3) . The fragmentation pattern in the MS of Azobechalcone reflects structure 1. Interflavonoid bond cleavage in (M+H)+ ion at 1503 accounts for abundant ions at m/z 1007 and m/z 615. The base peak at m/z 1129 comes from the rupture of the bond between carbons olt and Cip while other important ions at m/z 755 and m/z 619 are accounted for in Scheme 1. An all frans stereochemistry of the pentacyclic heterocyclic protons in l, was evident as corresponding protons to those in either lophirone C or mbamichalcone having practically the same chemical shifts and coupling constants are in an all PUKVstereochemistry. Confirmation came from NOE differences measurements in which no correlation spots were observed between: H,lI and HpI Hal2 and Hp2; and finally Hp2 and H,l2 Equally, protons Hc3 and Ha3; Hd3 and H,y3; Ha*3 and Hp3 show very faint enhancements in accord with a trans - rruns trans stereochemistry of the tetrahydrofuran ring. Biosynthetically, Azobechalcone can be considered to originate from the condensation of a unit each of lophirone C and lophirachalcone (6)
4124
G,
HZ7 O9 mlz
615
HO
C67H530,7
m/z
( M+H
1129
)+
C,,H71022
m/z
1503
CsaH,,0,5
m/z
1007
HO
Cd5Ha9 O,,
m/z
C38H35 OS,
755
m/z 619
Scheme 1: Major fragments in MS of 1 ACKNOWLEGDEMENTS: We thank MM. Nolt Internatiod
CRF’MT,
Foundation
Yaounde
of Science
for harvest and identification
(grant
1389/2) and DAGIC
of plant material.
This work was supported
(France).
REFERENCES: 1) A. E. Tih, R.Ghogomu
Tih, B.L. Sondengam,
M.T.Martin
and B.Bodo,
2) A. E. Tih, R.Ghogomu
Tih, B.L.Sondengam,
M.T.
and B.BodoJ.
R. Ghogomu
Tih, B.L. Sondengam,
4) A. E. Tih, R. Ghogomu
3) A. E. Tih,
Tih, B.L. Sondengam,
Martin
M.T. Martin M.T.
Martin
Tefmhedon
Leftem : 4 5, S797, (1988).
Nat. Products
and B.Bodo,
Phyfochemismy
and B.Bodo,
Phytochemisby
5) R. GhogomuTih,
B.L. Sondengam,
M.T.
Martin
and B.Bodo.
Phyfochemistry
6) R. GhogomuTih,
B.L. Sondengam,
M.T.
Martin
and B.Bodo.
Temhedon
: 5 3,964,
(1990).
: 3 1,981, : 3 1.3595,
: 28, 15.57, (1989). Leers
: 30, 1808, (1989).
(1992). (1992).
by